Liquid optically clear adhesives (LOCA) are becoming more prevalent in the display industry to fill air gaps between layers or substrates of a display module. For example, LOCAs are commonly used between the coverglass and indium-tin-oxide (ITO) touch sensors (FIG. 1a), between ITO touch sensors and the liquid crystal module (FIG. 1b), or between the coverglass and the liquid crystal module (FIG. 1c). The layers in the display configuration 2 of FIG. 1a includes a glass lens or plastic lens 10, a first liquid optically clear adhesive (LOCA) 12, a first ITO patterned circuit 14a, a double-sided ITO (DITO) glass plate 16, a second ITO patterned circuit 14b, a second LOCA 18, a front polarizer 20, a glass plate 22 and a back polarizer 24. The layers in the display configuration 4 of FIG. 1b includes a glass or plastic lens 26, an anti-splinter (AS) or anti-reflective (AR) coating 28, a LOCA 30, a front polarizer 32, a glass plate 34 and a back polarizer 36. The layers in the display configuration 6 of FIG. 1c includes a glass or plastic lens 38, a LOCA 40, a front polarizer 42, a color filter with ITO circuit 44, a glass plate 46 and a back polarizer 48.
The LOCAs are currently applied using a dispensable fluid or by patterning a thicker, potentially thixotropic, material with the use of a stencil or screen. The use of dispensable fluids involves flowable LOCAs that behave like a Newtonian fluid. To prevent flow beyond the desired printing area, the use of a pre-cured dam material is often required. When the optically clear adhesive is a LOCA, refractive index of the pre-cured dam material must match the refractive index of the LOCA. The use of a pre-cured dam material also involves an additional process step and may still lead to overflow of the LOCA if a precise amount is not dispensed and/or the co-planarity between the two substrates that are being bonded with the LOCA are not perfectly aligned.
The use of a screen for printing a LOCA has been described, for example, in U.S. Patent Application Publication No. 2009/0215351 to Kobayashi et al. The use of a stencil for printing a LOCA has been described, for example, in PCT Publication No. WO 2012/136980. Both methods require passing the LOCA through a screen or a stencil to properly apply the adhesive coating in the desired area on the substrate.
The methods mentioned above require printing and laminating one device at a time. For traditional dam and fill methods using a dispensable fluid, lamination must be done immediately after printing (or within a controlled amount of time after printing) because the LOCA flows over time. Current stencil printing and lamination processes for LOCAs also require vacuum lamination to remove bubbles from the viewing area.
Stencil printing/lamination LOCA equipment is expensive and typically has a Takt (cycle) time of about 60 to 90 seconds. To reduce cost, either the equipment cost per display must be reduced and/or the Takt time must be reduced. The limiting factor in the Takt time is the vacuum lamination step, which is often 2 to 3 times longer than any other step in the process. In addition, a significant amount of the equipment cost can be attributed to the vacuum chamber and pumps associated with it.